1. Field of the Invention
The present invention relates to an apparatus and cooling system particularly, but not exclusively, for use in the food or liquor industry.
2. Description of the Related Art
A known form of cooling system which is utilized in the dairy industry includes a ply heat exchanger for cooling milk from dairy cows to a temperature of about 4.degree. C., to inhibit bacterial growth whilst the milk is in a storage vat awaiting transport to a milk tanker. The bottom of the vat may be formed of a second "dimple plate" heat exchanger which is cooled by refrigerant or chilled water to maintain the milk at a low temperature. A mechanical agitator may also be provided in the vat to circulate the milk so as to maximize efficiency of the dimple plate heat exchanger, prevent separation of the milk particles and also to prevent stratification of the milk.
The plate heat exchanger is form of a plurality of thin plates which are connected in a sandwich type construction. Each plate has chilled water running through it for heat exchange with milk running over the plate. The manifold structure of the plate heat exchanger makes it prone to bacterial contamination. After each milking, the heat exchanger is taken out of line and flushed clean. Less frequently, the entire heat exchanger needs to be disassembled either for removing clogging deposits or for regulatory inspection. Assembly and disassembly of the plate heat exchanger is extremely labor and time consuming.
Aside from the above disadvantages, the conventional milking system has limited capacity for fluctuation in milk volume or flow rate due to limited supply of chilled water. The chilled water is obtained from a water tank, which may be cooled by refrigeration, or from an "ice bank" tank. The dimple plate heat exchanger may also be cooled by chilled water from either the water tank or ice bank tank. Known forms of ice bank tanks and water tanks for use in the above system have a large volume and are usually cooled to, for example, 0.degree. C. overnight to capitalize on offpeak power rates. The volume of the tank is generally sufficient to cater for a day's milking. However, when the amount of milk to be cooled is greater than normal, the capacity of the tank may not be sufficient, and the milk consequently may not be cooled to a low enough temperature. Further, the plate heat exchanger is generally constructed to cool a certain volume of milk over a predetermined time, i.e., at a given cooling rate. If the rate at which milk is collected from the cows is greater than normal, the milk will again not be sufficiently cooled. The capacity of the plate heat exchanger may be increased by connecting more plates to the beat exchanger but this is a rather complicated and time consuming process.
If the milk is not adequately cooled by the plate heat exchanger, supplementary cooling may be effected by the dimple plate exchanger on the bottom of the vat, but such cooling is not as efficient as the plate heat exchanger.
An arrangement is disclosed in GB 1465516 (Alfa-Laval Industrie-Technik GmbH, filed Jul. 14, 1973) where a two stage cooling process is utilized. Milk is firstly pre-cooled by an in-line heat exchanger and delivered to a vat, in a conventional manner. The pre-cooled milk is then recycled back through the heat exchanger after completion, or during interruption, of a milking operation to achieve a storage temperature of about 4.degree. C. The arrangement includes non-return valves for controlling fluid flow during each cooling stage.